Age-related decrease in energy expenditure at rest parallels reductions in mass of internal organs

Area of Science:

• Gerontology
• Human Physiology
• Metabolic Research

Background:

• Resting energy expenditure (EErest) declines with age.
• The specific factors contributing to this decline, particularly in elderly women, require further investigation.
• Understanding these factors is crucial for maintaining metabolic health in aging populations.

Purpose of the Study:

• To investigate the extent to which the mass of internal organs influences the age-related decrease in EErest.
• To compare directly measured EErest in elderly women with values predicted by equations derived from younger women.
• To elucidate the relationship between body composition, organ mass, and EErest in aging.

Main Methods:

• EErest was measured using the Douglas bag method in elderly women after an overnight fast.
• Body composition was assessed using an impedance method.
• Internal organ mass data were obtained from autopsy materials of women from relevant birth cohorts.

Main Results:

• A progressive age-related decline in EErest was observed, paralleling a reduction in internal organ mass.
• Fat-free mass (FFM) remained consistent between 65 and 75-year-old women but decreased in the 85-year-old group.
• Directly measured and predicted EErest showed a strong correlation in elderly women.

Conclusions:

• Modest reductions in metabolically active internal organ mass significantly contribute to the age-related decline in EErest.
• EErest in elderly women can be reliably predicted using body composition data and equations developed from younger populations.
• This research provides insights into the physiological mechanisms underlying metabolic changes during aging.